(Re)discovery of a mistletoe infecting the Cardón cactus

Abstract

85 T here are few known examples of cacti being successfully parasitized by other plants, such as mistletoes. This is surprising, because mistletoes infect numerous species of desert shrubs, many of which grow side by side with cacti. Two cases have been observed in South America: Tristerix aphyllus successfully infects Trichocereus chilensis in an area just north of Santiago, Chile1–3, and Ligaria cuneifolia infects plants of Corryocactus brevistylus growing near Arequipa, Peru4. In its second year, The Cactus and Succulent Journal printed an anonymous note stating that an unnamed parasite infected Echinocereus chloranthus near El Paso, but to our knowledge that has not been verified. The San Diego Natural History Museum has a photograph and two specimens collected by Reid Moran of the mistletoe Phoradendron brachystachym (formerly P. diguetianum) growing on both Pachycereus pringlei and P. pecten-aboriginum. On a field trip to Baja California Sur in 2007, Jon Rebman discovered plants of Pachycereus pringlei infected by large plants of Phoradendron brachystachyum. The infection does not appear to be widespread; only two infected cacti were seen on this field trip, and no infected cacti had been noticed on previous expeditions. This incidence of mistletoe/cactus infection appears to resemble that of the Ligaria/Corryocactus in that the mistletoe has numerous long branches and many green leaves. We do not know of any studies of this case of Phoradendron/Pachycereus parasitism. The phenomenon of mistletoe/cactus parasitism is rare—or at least rarely reported. We encourage anyone who does field work in cactus habitats to report any case they notice.